Musty split-level lower level
The family room in a 1960s split-level smells musty every summer, worse after rain, though there's no visible water.
Basements · Crawl spaces · Lower levels
Musty Basement and Crawl Space Odor Removal in Lakewood
A musty basement or crawl space is a clue, not just a smell. This guide helps Lakewood homeowners find what's causing it, understand how odor treatment works, and spot a moisture problem that has to be fixed first.
A Jefferson County guide to tracing basement and crawl space odors to their source before anyone treats them.
What a musty smell is telling you
Musty and mildew odors are typically produced by microbial growth (mold and mildew) on materials that stay damp. In basements and crawl spaces, that dampness comes from humidity, condensation on cool walls and pipes, exposed soil, minor seepage, or past water events that were never fully dried. Cardboard boxes, carpet, insulation, and the paper face of drywall are common places for odor to develop.
Air from a crawl space doesn't stay there. As warm air rises through a house, it pulls air up from below through gaps around pipes, wiring, and ductwork, so a crawl space odor often shows up in the rooms above it. Effective treatment addresses the odor-causing residue and identifies the moisture conditions that would bring the smell back.
Air from a crawl space doesn't stay there.
Go deeper on basement and crawl space odor
Longer explanations, worksheets and local notes for Lakewood homes.
How it works18
- Musty, sewer or gas: what kind of smell is coming from your basement?
- Why the lower level of a split-level smells musty every summer
- How crawl space odor gets into the bedrooms of a ranch house
Worksheets9
- A 30-day basement humidity and odor log
- Room-by-room walkthrough for finding a basement odor source
- Crawl space checklist: what you can learn from the access hatch
Is it a moisture problem or an odor problem?
This is the first question, and it changes everything. Odor treatment can't fix active moisture. If something is wet, it has to be fixed first or the smell comes back.
Moisture first if you see…
- Humidity readings above 60% that don't drop with a dehumidifier
- Damp spots, white crusty deposits (efflorescence) or water lines on walls
- Visible growth on drywall, wood or stored boxes
- Smell that gets worse after rain or snowmelt
Any of these points to a job for the right trade (waterproofing, drainage, plumbing or mold remediation) before anyone treats odor.
Odor treatment likely helps if…
- The space is dry by meter and humidity readings
- The smell is old: a past leak since repaired, stored items, old carpet
- It's concentrated in materials, not coming from a live source
- It came from a one-time event (smoke, a spill, an animal)
How basement and crawl space odor treatment works
Treatment focuses on both the odor and the conditions behind it.
- 01
Investigate
Inspect the basement and crawl space to find odor sources and signs of moisture or growth.
- 02
Assess materials
Identify which materials, like carpet, pad, insulation, or stored items, are holding odor.
- 03
Recommend
Explain what can be treated and what moisture, vapor-barrier, or mold issues need correction first.
- 04
Treat
Apply odor treatment to affected materials and perform whole-space treatment, including air pathways.
- 05
Prevent
Discuss dehumidification, vapor barriers, and storage changes that keep the smell from returning.
Lakewood basements and crawl spaces
Lakewood, west of Denver in Jefferson County, has a large stock of ranch homes and split-levels built from the 1950s through the 1970s, many with basements, crawl spaces, or both. Over the years, some have had minor seepage, plumbing leaks, or humidity issues that left odor behind, and many crawl spaces were built without modern vapor barriers.
Colorado's climate is generally dry, but basements and crawl spaces stay cool, and summer humidity can condense on foundation walls and cold-water pipes. A dehumidifier, a sound vapor barrier, and good storage habits go a long way, and treatment removes odor that's already built up.
- Neighboring Wheat Ridge, Edgewater, and Golden have many homes of similar age, with the same basement and crawl space questions.
- EPA guidance recommends keeping indoor humidity between about 30% and 50%.
- If a crawl space odor started with a leak or flooding, part of the cleanup may be covered by insurance; odor from long-term humidity usually isn't.
- If inspection finds active mold growth or water intrusion, it should be remediated or repaired before deodorizing.
ZIP codes served: 80226 (Denver), 80232 (Denver), 80214 (Denver), 80215 (Denver), 80227 (Denver), 80235 (Denver), 80228 (Denver).
Also nearby: 80219, 80204, 80223, 80033, 80236, 80212, 80211, 80202, 80203, 80110, 80002, 80218, 80209, 80419, 80123, 80210, 80206, 80205.
Common causes of basement and crawl space odors
Exposed soil or a torn vapor barrier in the crawl space letting ground moisture into the air.
High humidity in summer, when warm air meets cool foundation walls.
Old carpet or pad that got wet at some point and never dried completely.
Insulation in a crawl space that sagged, got wet, or was disturbed by animals.
Seepage at foundation cracks or window wells after storms.
Simple checks before you call
Aim for
30–50%
30–50%
An inexpensive hygrometer tells you more than your nose does.
Do
- Use an inexpensive hygrometer. Indoor humidity above roughly 50% encourages musty odors.
- Look through the crawl space access for standing water, bare soil, or fallen insulation.
- Move stored items off the basement floor and look for staining underneath.
- Pour water into floor drains you rarely use to refill the trap.
Don't
- Don't deodorize over active mold or a leak. It needs remediation or repair first, or the smell comes back.
- Don't count on a dehumidifier alone to remove odor already absorbed into carpet, insulation and stored items.
- Don't cover the smell with sprays or candles while the source is still there.
Lakewood basement and crawl space situations
Crawl space under a ranch home
A ranch home with a crawl space and no vapor barrier has a damp, earthy smell in the hallway and bedrooms above it.
Odor after an old leak
A water heater leaked two years ago and the carpet was dried with fans, but the musty smell never left.
Ask about a basement odor
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Basement odor questions
Does a musty smell mean I have mold?
Often, musty odors come from mold or mildew growth somewhere, even if it isn't visible. It can also come from damp materials, bare crawl space soil, or a dry drain trap. An inspection helps find the cause.
Will odor treatment get rid of mold?
No. Odor treatment addresses smell. Active mold growth should be removed through proper remediation, and the moisture source corrected. A careful odor provider should tell you if that's needed first.
How does a crawl space make the house smell?
Warm air rising through a home draws air up from the crawl space through gaps in the floor and around ducts and pipes. Whatever the crawl space smells like, the rooms above eventually do too.
Is crawl space odor covered by insurance?
If the odor came from a sudden covered event, such as a burst pipe that flooded the crawl space, related cleanup may be covered. Odor from gradual humidity or seepage usually isn't. Ask your insurer.
What humidity level should my basement be?
Keeping indoor humidity roughly between 30% and 50% helps limit mold and musty odors.
Will treatment require me to leave the house?
Whole-space treatments may require occupants to stay out of the treated area for a period. Ask for specific timing before scheduling.
Why does my basement smell like sewer only sometimes?
A common cause is a dry floor-drain trap. The U-shaped trap holds water that blocks sewer gas; if the drain is rarely used, the water evaporates and gas comes up. Pour a gallon of water into the drain. If the smell fades within a day, that was it. If it doesn't, a plumber should check for a cracked vent or line.